The present invention relates to a headlamp apparatus for a vehicle such as an automobile. More particularly, the present invention concerns a headlamp apparatus for a vehicle and a method of setting its optical axis position which make it possible to set the optical axis of a headlamp to a reference angular position with high accuracy in a headlamp apparatus equipped with a light-distribution controlling means for changing the illuminating direction or the illuminating range of the headlamp in a following manner in correspondence with the traveling conditions, e.g., an adaptive front-lighting system (hereafter AFS).
As the AFS which has been proposed to enhance the traveling safety of the automobile, a technique disclosed in JP-A-2002-160581 proposed by the present applicant is known. In this AFS, information indicating the traveling conditions of an automobile CAR is detected by sensors 1, and their detection outputs are outputted to an electronic control unit (hereafter ECU), as shown in a conceptual diagram in FIG. 1. As the sensors 1, there are provided, for instance, a steering sensor 1A for detecting the steering angle of a steering wheel SW of the automobile CAR, a vehicle speed sensor 1B for detecting the vehicle speed of the automobile CAR, and vehicle height sensors 1C (only the sensor for the rear axle is shown) for detecting the respective height of front and rear axles for detecting the horizontal state (leveling) of the automobile CAR. These sensors 1A, 1B, and 1C are connected to the ECU 2. On the basis of the outputs from the inputted sensors 1, the ECU 2 controls swivel lamps 3R and 3L respectively installed on the left- and right-hand sides of a front portion of the automobile, i.e., headlamps 3 whose light distribution characteristics can be changed through deflection control of the illuminating direction in the left-and-right direction. As such a swivel lamp 3R, 3L, one is known which is equipped with a rotatively driving means for rotatively driving a reflector or a projector lamp provided in the headlamp by a driving source such as a drive motor as a construction capable of rotating the reflector or the projector lamp in the horizontal direction. The mechanism including this rotatively driving means is called herein an actuator. According to this type of AFS, when the automobile travels on a curved road, it becomes possible to illuminate the road ahead of the curve in correspondence with the traveling speed of the automobile, which is effective in enhancing the traveling safety.
To realize appropriate illumination in such an AFS, it is necessary for the steering angle of the steering wheel and the deflection angle of the swivel lamp to correspond to each other properly. When this correspondence fails to be obtained, the following problems of traveling safety occur: Namely, it becomes impossible for the beam of the swivel lamp to illuminate the direction desirable for the traveling direction of the automobile, e.g., the road ahead when the automobile travels straight ahead or around a curve, or the beam is deflected toward the opposite lane and dazzles the driver of an oncoming vehicle.
For this reason, with the conventional AFS, when the ignition switch of the automobile is turned on, initialization is carried out whereby the swivel lamp is oriented to a predetermined reference angular position, normally in a straightly advancing direction of the automobile. If such initialization is carried out, it becomes possible to obtain correspondence between the steering angle of the steering wheel SW and the deflection angle of the swivel lamp, and it subsequently becomes possible to effect appropriate deflection operation of the swivel lamp by using this initialized reference angular position as a reference. Incidentally, to initialize the swivel lamp, it is necessary to detect the present deflection angle of the swivel lamp. For this reason, this type of actuator is conventionally provided with a deflection angle detector for detecting the deflection angle of a rotating output shaft of the actuator which is in a corresponding relationship with the deflection angle of the swivel lamp. For example, a potentiometer is disposed for the output shaft of the rotatively driving means for rotatively driving the swivel lamp, and the rotational angle of the output shaft, i.e., the deflection angle, is detected from the output of this potentiometer.
However, the provision of such a potentiometer constitutes a factor making the structure of the actuator complex and large in size, and is therefore unfavorable. For this reason, it has been conceived to detect the deflection angle of the swivel lamp by detecting the rotational angle of the drive motor which is a driving source of the rotatively driving means of the actuator. Hall elements or Hall ICs (hereafter referred to as Hall elements) for outputting pulse signals in a number corresponding to the amount of rotation of the drive motor have been used as a rotational-angle detector designed for this purpose. Namely, as the pulse signals from the Hall elements outputted in conjunction with the rotating operation of the drive motor are counted, the deflection angle of the actuator is indirectly detected so as to realize appropriate control of the AFS.
In addition, the initialization of the swivel lamp is conventionally effected by making use of the pulse signals from the Hall elements. For example, the swivel lamp is rotated until it abuts in one direction, i.e., upto the position of the maximum deflection angle. At the same time as the swivel lamp is rotated from this rotational position in the opposite direction, the counting of the pulse signals from the Hall elements is started, and the rotation is stopped when predetermined pulse signals have been counted. Accordingly, if the correlation between the count of the pulse signals and the deflection angle of the swivel lamp is determined in advance, it becomes possible to rotate the swivel lamp from the abutment position by a predetermined deflection angle on the basis of the count of the pulse signals. Thus it becomes possible to set the swivel lamp to a predetermined reference angular position, i.e., in the straightly advancing direction in this case.
Incidentally, the present inventors have studied the application of this type of AFS to an automobile equipped with a leveling mechanism, i.e., an automobile equipped with a leveling mechanism for detecting the inclination of the automobile in the vertical direction by detecting the vehicle height concerning the front wheels and rear wheels of the automobile and for adjusting the deflection angle of the headlamp in the vertical direction in correspondence thereto. Moreover, in this case, the present inventors have also studied the setting of the swivel lamp to a reference angular position in the vertical direction at the same time as the setting in the left-and-right direction during the initialization of the swivel lamp. For example, this is an attempt to set the swivel lamp to reference angular positions in the left-and-right and vertical directions by operating the leveling mechanism at the same time as the actuator for setting the reference angular position in the left-and-right direction is operated. Here, the horizontal direction is normally selected as the reference angular position in the vertical direction.
However, in the case where an attempt is thus made to simultaneously effect the setting of the reference angular positions in the left-and-right direction and the vertical direction, there are cases where the optical axis of illumination is oriented toward the oncoming vehicle side at the time of setting the reference angular position of the swivel lamp in the left-and-right direction. At this time, if the optical axis of illumination of the swivel lamp in the vertical direction is oriented in the horizontal direction or a direction higher than that by the leveling mechanism, there is a possibility of dazzling the driver of the oncoming vehicle. Accordingly, it is required to initialize the swivel lamp in a state in which the dazzling of the oncoming vehicle is prevented.